New Theory on Origin of Evolutionary Traits in Early Hominins

Diana Rabenold, a graduate student working on her Ph.D. in Anthropology is challenging conventional wisdom about the diet of Paranthropus boisei, a large-toothed species of early hominid found in East Africa between 1.4 and 2.5 million years ago.

In a paper published in PLoS ONE this week, she and one of her advisors, Associate Professor of Anthropology Osbjorn Pearson, argue that P. boisei may have had a diet that included many more abrasive foods such as grasses and reeds that were softer than expected.

Anthropologists base their conclusions about the diet of early hominids on the only evidence that usually remains, the teeth. Rabenold says one of the great puzzles of paleoanthropology is why some primates, including fossil hominids, have thick enamel, and others do not.

Paranthropus boisei had very thick enamel. Rabenold and Pearson argue that thick enamel evolved to consume plants with large amounts of phytoliths. Phytoliths are microscopic bits of silica that plants draw from water in the soil and deposit in their tissues. The silica is extremely abrasive; Rabenold and Pearson believe that Paranthropus boisei evolved thick enamel in their teeth to cope with dental abrasion from the silica in the plants.

Rabenold's hypothesis is "the amount of phytoliths in foods correlates with the evolution of thick molar enamel, although this effect is constrained by a species' degree of folivory." Her research assembled detailed tables of various primate species and the percentage of plants that have been identified in the diet of each, along with numbers showing the amount of phytoliths in the diet. The initial findings of Rabenold and Pearson show the amount of phytoliths and leaves (which exert a different pressure to evolve sharp crests and thin enamel on teeth) in the diet correlate strongly with the thickness of molar enamel.

Rabenold plans to expand on this research for her doctoral dissertation, in collaboration with her advisors, Drs. Sherry Nelson and Osbjorn Pearson.